1. Field of the Invention
The present invention relates to a lighting device implemented through utilizing an insulating type piezoelectric transformer in driving light-emitting-diodes (LEDs), and in particular to a lighting device implemented through utilizing an insulating type piezoelectric transformer in raising power conversion efficiency, so as to optimize the lighting efficiency of the light-emitting-diodes (LEDs).
2. The Prior Arts
In recent years, the tendency of development of information-related products is toward light weight, thin profile, and compact size, so that it is becoming increasingly popular and common in utilizing piezoelectric transformer in driving backlight unit of liquid crystal display (LCD). The basic design principle of piezoelectric transformer is that: the energy exchange and conversion effects between electrical field and mechanical field are used to transform power voltage, thus it has the various advantages of compact size, light weight, high electrical energy conversion efficiency, high reliability, high insulation capability, and without electromagnetic interference (EMI) radiation. However, as the primary side of the piezoelectric transformer is used to receive a driving voltage and output a voltage with a transformation ratio from a secondary side, and in case that the piezoelectric transformer is driven by signals at a non-resonance frequency range, then the piezoelectric transformer tends to produce parasitic oscillations. In this way, the secondary side may output power of non-resonance frequency, yet it will consume energy and lower the power conversion efficiency of piezoelectric transformer.
In the prior art, a piezoelectric transformer achieves insulation of its primary side and secondary side by means of a conventional coil-winding type transformer. Since a coil-winding transformer may produce sine wave output voltage higher than that of the input voltage, therefore, sine wave voltage of non-resonance frequency is used to drive a piezoelectric transformer, so as to realize its advantages of increased power conversion efficiency, and that the driving circuit of piezoelectric transformer can be driven with a lower voltage. However, in the prior art, a coil-winding type transformer can be used for voltage transformation, therefore, the size of the entire driving device appears to be enormously large, and that is not compatible with the modern requirement of light weight, thin profile, and compact size. In addition, in performing voltage transformation, the coil-winding type transformer is liable to have magnetic core efficiency loss and thus its power output efficiency is reduced; moreover, the voltage endurance of coil winding is rather insufficient, such that it is liable to be broken through due to suddenly electric jump of power supply to a high voltage, thus resulting in short circuit and being burned out, as such it is highly hazardous.
In the prior art, the LEDs are lighted by the DC source with the charge pump circuit. However, when the amount of the LEDs increases, several integrated circuits with charge pump function have to be adopted. The cost price of the integrated circuit is high in the total driving circuit. Thus, the driving circuit of the large size of the LED panel is difficult to reduce the price.